1. Field of the Invention
The present invention relates to a system for supplying fuel to the cylinders of an internal combustion engine such as a gasoline engine or a diesel engine.
2. Description of the Related Art
In an internal combustion engine including a plurality of cylinders, fuel distributor pipes such as delivery pipes (also called a common rail) are known for supplying fuel directly or indirectly (through a precombustion chamber or an intake port) to the respective cylinders.
Such fuel distributor pipes serve to distribute fuel fed under high pressure from a fuel pump as a fuel supply source to fuel injection valves provided in the respective cylinders.
To carry out the above function, since the fuel distributor pipes are provided in the vicinity of the internal combustion engine, they are likely to be influenced by heat generated in the internal combustion engine. That is, the fuel supplied to the fuel distributor pipe is heated, increasing its temperature.
This increase in the fuel temperature becomes greater as the time required for the fuel to pass through a fuel path of the fuel distributor pipe becomes longer. These fuel distributor pipes have different branch positions from which fuel is supplied to the respective cylinders. Accordingly the temperature of the fuel supplied to the respective cylinders may vary from cylinder to cylinder.
The fuel injection valves for injecting the fuel distributed from the fuel distributor pipes adjusts the amount of the fuel to be supplied to the respective cylinders according to its opening degree. The fuel injection valves adjust a fuel amount according to volume, not weight. Therefore as a fuel temperature is increased, an amount of fuel supplied to a cylinder is decreased owing to thermal expansion of the fuel.
If the temperature of fuel supplied to each cylinder is increased at the same rate, the fuel amount can be corrected using feedback control, which causes no problem. If the fuel temperature varies depending on the cylinder to which the fuel is supplied, the fuel amount cannot be corrected with respect to all cylinders. This may result in a failure to supply the correct amount of the fuel to each of the respective cylinders.
As a result, output torque varies depending from cylinder to cylinder, which may cause variations in the revolution of the internal combustion engine.
Japanese Patent Application Laid-open No. HEI 5-240122 discloses a technique for reducing difference in fuel temperature between two delivery pipes disposed in each bank of a V-type 6-cylinder internal combustion engine. This technique however, is effective for reducing differences in the fuel temperature between different delivery pipes but not for reducing differences in fuel temperature between cylinders in the same delivery pipe. This technique fails to suppress or prevent variation in the revolution of the internal combustion chamber owing to the difference in the fuel temperature among cylinders.
Japanese Patent Application Laid-open No. HEI 6-323220 discloses a technique for fuel supply to a delivery pipe between third and fourth cylinders of a 6-cylinder internal combustion engine, and Japanese Patent Application Laid-open No. HEI 6-58219 discloses a technique for fuel supply to both sides of a delivery pipe of a 6-cylinder internal combustion engine. The aforementioned techniques, however, fail to sufficiently suppress or prevent variation in revolution of the internal combustion engine. Further, Japanese Patent Application Laid-open No. HEI 5-33741 discloses a technique for cooling the fuel that has not been injected through the injector and returned to the fuel tank. However, this technique fails to overcome the difference in the fuel temperature among cylinders, which cannot suppress or prevent variation in revolution.